1. For the cooking: Pulse sugar and zest in food processor until blended, about 5 - 7 pulses. Transfer to medium bowl.

2. For the doughnuts: Heat 3 inches of vegetable oil in 4-quart saucepan until temperature reasches 350 degrees. Whisk flour, baking powder and salt together in a medium bowl. Whisk eggs, sugar, and orange zest in a large bowl. Whisk in lychee syrup, then butter, until well blended. Stir in the flour mixture until evenly moistened.

3. Preparation: Using two dinner teaspoons, carefully drop heaping spoonfuls of batter into the hot oil. Fry, maintaining temperature between 325 and 350 degrees, until doughnuts are crisp and deeply browned on all sides, 3 to 6 minutes. Using a slotted spoon, transfer the doughnuts to a plate lined with paper towels. Drain for 5 minutes.Add doughnuts to the bowl with orange sugar and toss until well coated. Place on a serving plate and repeat with the remaining batter, regulating oil temperature as necessary. Doughnuts are best served warm.